Apparatus sensitive to magnetic fields



M 19', 1949. 1.. F. BEACH 2,476,273

APPARATUS'SENSITIVE TO MAGNETIC FIELDS I Filed Sept. 17, 1942 2 Sheefcs-Sheet 1 PHASE DETECTO R FREQ 26 nm In DOUBLER T 1111' l l2 a Is IAMPLIFIER INVENTOR LENNOX F. BEACH;-

sAT'FoRNY.

July 19, 1949. L. F. BEACH APPARATUS SENSITIVE TO MAGNETIC FIELDS 2 Sheets-Sheet 2 Filed Sept. 17, 1942 PtWMM/EAIT 75 MAGAIEZ O m w r R r R 0 R ET m m M WDM D LN WNM m FE R A W, L M AUR o MQW. A M

INVENTOR, LENNOX F. BEACH; gLiLfl M HIS A'I TORNEY.

Patente giJuly 19, 1949 Lennox F. Beach, Merrick, N. Y., a ssignor to ,Purves Corporation, Springfield, Mass.,'a corporation of Massachusetts Application September 17, 1942,sena'1 No. 458,739

13 Claims. (Cl; 177-351) 1 This invention relates to magnetic field responsive devices and it refers more particularly to devices whose operation depends upon the non-linear magnetic characteristic of a career cores of permeable material carrying the fiux of the field.

Indicating and power controlling devices whose ration characteristic of iron or the more permeod of operation described, in U. S. Patent No.

1936, and in the copending applications of the 30, 1940, which matured into U. S. Patent No. 2,383,459, issued August 28, 1945, and Serial No.

U. S. 'Patent No. 2,383,460, issued August 28, 1945,, said last application being joint with John C. Purves, and both of said applications being assigned to the assignee of the present invention.

Devices of the characterreferred to, sometimes known as flux valves, include an inductor member or a plurality of inductor members, each comprising a core of ferromagnetic'material to which a periodically variable magnetomotive force is applied by means of an exciting winding or windings and having an output winding in which an E. M. F. is induced due to the combined action of the exciting fiux and the flux the. core. In some instances, a single winding An important application ofthe flux valve type i of apparatus is in themeasurement or the indi- 1 cation of the directionof the horizontal component of the earths-magnetic field.

' an alternating potential at double the frequency of variation of the exciting current and to, obtain reliable and accurate operation, particular- 1y at low outputs, it is necessary to eliminate, ;by balancing or filtering, any component of exciting frequency which-appears in the output. To avoid the use of filters, the present invention in certain of its embodiments provides for a simple mechanical adjustment of elements which is efthe frequency of the exciting flux.

Other factors adversely afiecting reliability of operation of prior fiux'valve devices, particularly a uniformity of'output' with repeated occurrence of the same magnetic fieldconditions, are the existence of a unidirectional magnetic bias in a portion of the inductor core material (which may operation depends upon the non-linear Or satuable ferrous alloys are disclosed, and their meth- 2,047,609 to Haig 'Antranikian, dated July 14,

present applicant, Serial No. 348,582, filed ,July

385,622, filed March 28, 1941, which matured into of the field in producing periodic saturation of carries both the exciting and output currents.

In most flux valve devices the utilized output is the present invention avoids these defects by shift the operating point elongate magnetizatlon curve) and an unequal degree of saturation in different portions of such material. Both conditions, result from failure to apply the exciting magneto-motive force in a manner which causes all portions of the core material to experience periodic reversals of fiux ofthe same amplitude. The construction of theinductor of applying to the inductor core'an exciting alternating magneto-motive force producing a nearly uniform fluxdensity throughout the core.

The maximum electrical output of a saturable inductor subjected to a uniform magnetic field is very nearly proportional to the length of the inductor and for a given length'the maximum emciency is obtained by subjecting the entire core material to a uniform degree of saturation corresponding to the most favorable operating point on' the magnetization curve. The inductor of the present invention is highly eflicient from' both these viewpoints since its length is great in proportion to the magnetic material-used. and the excitation of the core material is uniform throughout and maybe adjusted to an optimum operating condition.

Certain magnetic field-sensitive devices have employed an inductor with a "window" or openv ing through which the exciting or output winding or both must be threaded, which is a tedious and uneconomical manufacturing operation.

The construction of the inductor, according to the present invention, is such that all windings may be-put on the core elements by ordinary coil winding apparatus without any threading operation; thus reducing manufacturing costs.

It is an object of the present invention to provide a flux valve inductor of simplified construction adapted for economical manufacture.

It is a primary object of this invention to provide a flux valve, or an electrical inductor defective in balancing out any component output at t vice, having three core legs of permeable'magnetic material, an exciting-winding, and pickup coils associated with the respective core legs, the

pickup coils being Y connected in a three-circuit alternating output whereby the device will function, through interaction with a unidirectionalmagnetic field to provide a three-circuit, variable alternating potential output similar to that of a Selsyn transmitter which is adaptedto be used in. reproducing the.,position of the core legs in the magnetic field by connecting the output of the device to an induction device of the Selsyn type.

Another object is to provide an inductor which I 3 is highly efiicient as to utilization of core material and space occupied for a given output.

Another object is to provide an inductor suitable for applications where space and weight are restricted, such as in gyroscope mounted or glmbal suspended pick-ups.

Another object is to provide an inductor where-. in a simple mechanical adjustment may be made to balance out the effect of exciting current on the output.

Another object is to provide an inductor wherein the entire core structure is subjected to a substantially uniformalternatlng exciting flux thereby increasing the emciency of the inductor and furnishing a device of stable and reproducible sensitivity.

Another object of the invention is to provide an electrical balancing adjustment in the exciting circuit of a flux valve of the type having a divided core inductor and a divided exciting winding.

A further object is to provide an improved magnetic field-sensitive pick-up suitable for supplying actuating electrical impulses to remote indicating or power controlling devices, or to torque exerting means for precesslng a gyroscope.

Still another object is to provide a magnetic compass of the stationary inductor type having improved pick-up means.

Other objects and advantages will become apparent as the description proceeds.

In the figures,

Fig. 1 is a broken view of an improved inductor according to the invention.

Fig. 2 is a sectional view taken along line 2-2 of Fig. 1. I

Fig. 3 is a wiring diagram of a single inductor according to the invention, connected to an indicator.

Fig. 4 is a diagrammatic showing of an inductor, adjustable to effect an inductive balance.

Fig. 5 is a wiring diagram of a gyro-stabilized inductor assembly connected to control a remote servo device.

Fig. 6 is an elevation of the stabilizing gyro-. vertical of Fig. 5 with the inductor assembly mounted thereon.

Fig. 7 is a perspective view of modified adjust able inductor according to the invention.

Fig. 8 is a section taken transversely of the inductor illustrated in Fig. 7. a

Fig. 9 is adiagrammatic view of a pair of crossed inductors according to' the invention connected to a crossed-coil indicator.

Fig. 10 is a wiring diagram of the apparatus of Fig. 9. a

In the figures, particularly Figs. 1-3, an inductor III is shown comprising a pair of elongated core members ll, l2 ofequal length and of rectangular cross section positioned parallel to and spaced from one another. These core members may be of fpermalloyfi mumetaP' or other ferromagnetic material of high permeability, it being particularly desirable to employ material exhibiting a'sharp bend or knee in the magnetization curve. As an illustration of the size of these core members or strips, in certain successfully tested devices, a thickness of .020" has been used with a width of approximately one quarter of an inch and a length of approximately two inches. Core member H is surrounded throughout substantially its entire length by a uniform exciting winding i5 which is adapted to apply a substantially uniform magnetizing force (magneto-motive force per unit distance) along the core axis, While core member i2 is surrounded e by a similar exciting winding l5. As illustrated, the sections of cores II and I2 are uniform throughout their respective lengths and therefore. due to the uniform exciting windings, the same flux density is obtained in all portions of a core at a given instant. If variable section cores are used. the exciting winding may be designed to produce inversely varying magnetizing forces.

Cores II and I! are spaced from one another as by end spacers It or other separators of nonmagnetic material, although spacers of magnetic material at the ends of the cores, only, may be used to increase the efllciency of the device somewhat. The use of such magnetic spacers, however, has the disadvantage of the possibility of non-uniform sensitivity due to random changes of reluctance of the joints in the magnetic circuit. The separation of the cores is exaggerated in the figures clearly to distinguish the several windings of the inductor.

A pick-up or output winding l I completely surrounds the assembly of cores H and I2 and their respective exciting windings and is preferably symmetrically positioned with respect to the centers of these cores. Winding l1 may or may not extend over the entire length of the cores. A slight balancing adjustment to compensate for inequalities of the two exciting windings may be secured by relatively shifting cores II and 12 before secondary winding I1 is put on. However, more efllcient balancing arrangements are shown in Figs. 3 and 4, to be described.

In the wiring diagram of Fig. 3 exciting windings I5 and 15' are connected in series and in a manner to produce magneto-motive forces in opposite directions in cores II and I2 when connected to the same source of alternating potential 20, as by way of potential divider M. A potentiometer 22 having an, adjustable contact 23 is provided for equalizing the excitation of the two cores, equalization being evidenced by the tial supplied from source 20 byway of frequency doubler 25. v

It is known in the operation of flux valve devices that the phase of the alternating output potential reverses when the direction of the field reverses with respect to the normal to the magnetic axis of the inductor member. To detect thisphase change and obtain a unidirectional potential reversing in polarity in correspondence therewith, any one of a number of phase sen sitive devices known in the art may-be employed. One such device is illustrated in the above referred to applicationNo. 348,582, now U. S. Patent No. 2,383,459.

Frequency doubler 26 in the A. C. biasing circuit of device 25, which may be of conventional known design, is included since the utilized electrical output of the flux valve is at double the frequency of the exciting supply. A suitable indicator such as zero-center D. C. meter 21 is connected to the output of phase detector 25 to indicate the direction and magnitude of the magnetic field. 1

Inductor ill, used as a compass, may be mounted I directly on a mobile craft such as an airplane,

in which case by orienting inductor ID with its magnetic axis perpendicular to the longitudinal axis of the craft zero center meter 21 may be caused to indicate the magnetic heading of the craft or the inductor may be mounted on a rotatamama I able support :5 (Fig. 3) and manually positioned to give a null or amaximum indication-on meter 21, the direction'of the field being'perpendicular I to the inductor axis if the null indication is used and parallel to said axis if the maximum indica-' tion is used. Support may also be caused to be self-orienting by means similar'to those disclosed 1 in my aforementioned application Serial No. 348,582, now U. 5. Patent No. 2,383,459.

f In Fig. 4 anarrangement is illustrated which dispenses with the balancing potentiometer 22 of Fig. 3 by providing a'pa'ir of core members l2 of unequal length. As before described, each core carries a uniformly wound exciting winding, as l5, l5, which extends over substantially the entire length of the core. Whencore l2 is'symmetrically positioned with respect to the center-.01 core- H and magnetic conditions are uniform throughout the two cores, no output component at exciting frequency will appear in winding H. To locate this central position or rather to'eflect an inductive balance that compensates for any slight magnetic irregularities which may cause an exciting frequency component to appear in the output when winding I1 is geometrically symmetrical with respect to windings l5 and I5, core I coil I1 is wound over the cores II, I! by slipping an exploring or test coil over the cores and, with the cores normally excited, making a suitable axial adjustment to reduce the exciting frequency component in the test coil voltage to zero, then immobilizing the two cores .relative to one another, removing the test coil and applying output winding Alternatively the output coil, and also if desirable the exciting coils, may be wound on supports which are slidably adjustable with respect to the cores and the members of the assembly fixed in position after a balance is reached.

In- Fig. 5, there is shown a combination of three inductors 30, 3| and 32, preferably of the previously described -constructin, positioned with their respective magnetic axes, at equal angles one to another in a, plane to form a pick-up device 35 mounted on a stabilizing gyro-vertical 33. Device'35 supplies a three-component electrical output adapted to actuate a remote receiver 36 of the selsyn type. Receiver .36- comprises a three winding stator 31 and a single winding rotorv 38 and is operated as a constrained rotor device, sometimes referred to as a signal generator or synchro transformer." Receiver 35 is connected to furnish a single phase alternating potential signal to an amplifier 40, which may be of conventional design, whose output operates a motor 4| to position a device 42 in relation to the direction of the magnetic field actuating pick-u'p 35. A repeat-back connection 42 to rotor 38 of se1syn" 36 is provided by shaft 45 geared to the motor shaft.

Gyro verticals such as 33, are well known devices employing gravity controlled erection means, as 48, to maintain the spinning axis of a gyro in a vertical position. By a suitable mounting on a. gyro, the assembly of inductors 30, 3| and 32 may be stabilized in a selected plane as, for example, the horizontal, the inductor outputs be- Lng proportional to components of the magnetic field insaid plane. When stabilized in the horizontal plane, as in a compass pick-up, the outputs from the three inductors are proportional to three symmetrical components of the horizontal component 'of the earth's magnetic field. In addition. to its use'as a compass pick-up, the 5' described plane assembly of 'a plurality of inductorsfinds numerous other applications including the fields of the stabilization of aircraft, sensitive instrument repeaters; etc.

Instead of operating motor, the output of amplifier 40 may be used to actuate torque'exerting means for precessing a directional gyroscope to a position corresponding tothe direction of ,the earth's field, to which pick-up 35 is subjected. Such an .arrangement, utilizin inductors of a different type, is shown in my copendingapplication Serial No. 414,422,-fi1ed October :10, 1941, joint with O. E. Esval and others, which matured into U. 3. Patent .-No. 2,383,461, issued August 28, 1945.

Figs. 7 and 8 illustrate a modification of the inductor of the invention in which an inductive balance between the two primary exciting windings and the output winding is obtained by diiferentially changing the number of turns of afcontinuous conductor constituting the primary windings. In this modification, cores of cylindrlcal form are preferably used, as 50, 5|, rotatably mounted on a frame 53. A continuous conductor oppositely wound on the two cores has different portions forming the two exciting windings 54 and 55 therefor. A terminal of this continuous conductor is fixed on each of the cores and connections brought out to an external circuit by way of contact members 51, 58 and respectively cooperating brushes 59, 60. Surrounding the two cores is output coil 61 wound on a supporting frame 68. Due to the opposite winding of the primary coils 54, 55, these coils are oppositely inductively related to coil 67. Cores 50 and 5| are prevented from free rotation by the friction of their bearings in frame 53, a screw driver adjustment, such as slots 63, being provided for rotating one core or the other to effect an inductive balance. A balance is made by supplying alternating current to windings 54 and 55 by way of brushes 59 and6|l and contact members 51, 58 to produce a selected degree of saturation in cores 50, 5| and by connecting indicating means to coil 61, sensitive to'the exciting frequency component which appears in that coil due to unequal mutual inductances between coil 61 and coils 54 and 55, respectively. An adjustment is then made by rotating one or the other of cores 50, 5| until such exciting frequency component is reduced to zero or minimum.

It will be apparent that counter-clockwise rotation of core 50, for example, causes a simultaneous increase of the number of turns in coil 54 and a decrease of the number of turnsin coil 30 55, thereby differentially altering the mutual inductances of said two coils with respect to coil 51in one direction, while similar rotation of core 5| differentially alters the mutualinductances in the opposite direction.

Fig. 9 shows a combination of a pair of crossed inductors, of the improved construction dis-"- 4 closed herein, and a crossed coil indicator in which the two pick-up or inductor output coils are switched in rapid alternation to corresponding indicator coils, thus rendering the device operative along only one inductor axis at a time. The pick-up I3 is shown as comprising inductors l0 and 1| positioned with their magnetic axes at right angles to one another for supplying outputs 76 respectively proportional to relatively perpendicular components of a magnetic field while the indicating device I8 is shown as comprising a pair of stationary coils I4 and." likewise positioned with their magnetic axes perpendicular with one another and a permanent magnet I8 mounted on a vertical spindle passing through the intersection of the axes of coils 14, ii for actuation by said coils to a position corresponding to the direction of said field.

A pointer 11 (shown, for cleamess, at a angle to the magnet) is mounted above magnet 16 on the magnet spindle for indicating bearings on a graduated card I8.

The switching means is better seen in the wiring diagram of Fig. 10. Vibrator 80 has its exciting coil BI connected to D. C. source 88 in series with exciting windings 85 and 88 of inductors l and II respectively, here illustrated as parallel connected. It will be understood from the description of the preceding figures that each winding 85, 88 has portions oppositelywound on two spaced cores, one above the other, corresponding to windings I and I5 of Fig. 1.

Excitation of coil 8| attracts an armature 88 which eventually engages contact 89 and short circuits coll 8|, thereby deenergizing said coil and permitting armature 94 to return to its unoperated position. The repetition of the described cycle of events which includes the shortcircuiting of coil 8| causes a pulsating unidirectional current to flow in windings 85 and 88 for saturating inductors I0 and 'II and rendering them sensitive to a magnetic field. Output windings 93 and 94 of inductors I0 and II, respectively, have a terminal of each connected to junction point 95, connected by lead 96 to phasesensitive amplifier-modulator I00 of known design. The opposite terminals of windings 93 and 94 are connected to vibrator contacts 91 and 98 respectively. A rocker arm I02 rotated in correspondence with, and about the pivot point of, armature 88 carries a pair of contact arms I03, I04 insulated from armature 88 and from each other. Arm I03 is adapted upon displacement from its unoperated position to make contact with one of contacts 91. 98 and is connected by lead I06 to the input of amplifier I00. Oscillation of arm I03 therefore serves to switch windings 93 and 94 alternately to the input of amplifier I00 in synchronism with the pulsations of exciting current produced by the short-circuiting of vibrator coil 8|.

Contact arm I04, connected by lead I05 to the output of amplifier I00, upon oscillation by rocker I02 makes contact in alternation with contacts I01 and I08 which connect with terminals of coils I4 and 15 of indicator I8, respectively. The opposite terminals of these coils 14 and I5 are joined at a common point I09 and connected through a common lead to the output of amplifier I00. Oscillation of arm I03 therefore serves to switch the output of amplifier I00 to indicator coils I4 and 15 in synchronous alternation with the switching of coils 93 and 94 to the input of the amplifier, coil 93 being connected to the amplifier input circuit when coil 14 is connected to the output and similar correspondence obtaining between coils 94 and I5.

An additional contact arm H0 in electrical connection with arm 88 and operated therewith may be employed in cooperation with a contact III to supply interrupted current from source 83 over leads II2 to amplifier-modulator I00 to render this dev ce sensitive to the phase of the input potential thereto.

Amplifier-modulator I00 is a phase-sensitive device, such as device 25 of Fig. 3, of a type well known in the art, which supplies a unidirectional output whose polarity reverses with reversal of the phase of an input alternating potential. Such circuits require a source of reference phase. By the described arrangement of contacts on a single vibrating element the alternating components of the inductor exciting current and the current supplied over leads II2 are of the same frequency and maintain a constant phase relationship. I have found that the current supplied over leads II2 may be used directly to render amplifier I 00 phase sensitive. However,

since the outputs of pick-up coils 83, 94 is at double the exciting frequency, the apparatus designated generally by the block I00 preferably includes means for doubling the frequency of the alternating component oi the supply by way of leads II2.

Since the moving system of indicator I8 has a certain amount of inertia, magnet I6 and pointer TI will provide a steady indication of the resultant of the fields set up in coils I4 and I5 by the direct current output of amplifier I00 ii vibrator 80 operates at a sufliciently high rate. The position of pointer 'II may be read on graduated card I8.

Among other advantages, the arrangement of Figs. 9 and 10 uses the same amplifying elements to supply current to coils 14 and I5 and thereby eliminates errors due to differential amplifier changes in a system of the type described. Vibrator 80 may be of simple design such as is used in plate supply circuits for automobile radio sets and the current supplied over leads II2 may furnish plate current for amplifier I00. The circuit being operated entirely from a D. C. source finds many applications where alternating potentials are not available.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. Having described my invention, what I claim and desire to secure by Letters Patent is:

1. In apparatus sensitive to an external ma netic field for supplying a voltage output dependent in magnitude upon the direction of said field relative thereto, an inductor comprising a pair of elongated laterally spaced magnetic core members of unequal length, a source of alternating potential, a winding on each of said members connected to said source, each of said windings being constructed and arranged to apply a uniform magnetizing force along substantially the entire length of the core member with which it is associated and a third winding surrounding both of said core members, said members being relatively positioned to produce equal and opposite mutual inductance between the respective exciting windings thereupon and said third winding said third winding being adapted to supply as an output a potential induced therein through interaction between said inductor and the external field.

2. In a device sensitive to an external magnetic field for supplying a voltage output depending in magnitude upon the direction of said field relative thereto, a pair of spaced core members of permeable, magnetic material, a continuous conductor having portions thereof coiled about each of said core members, said conductor being arranged and adapted to produce, when energized from a source of periodically varying current, a periodically varying flux flowing in relatively opposite directions in said core members, respectively, for instantaneous values thereof, adjustable means for simultaneously uncoiling said conductor from one member of said pair and recoiling it about the other member, connecting means for supplying current to said conductor from,a source of periodically varying current, and a pick-up winding surrounding both of said core members whereby potentials of a frequency equal to the periodicity of. said varying flux will be substantially balanced out in said pick-up winding while alternating voltages produced through interaction between said device and external field and of a frequency twice that of the periodicity of the flux variations will be provided'as a signal output by said pick-up winding.

3. In a device sensitive to an external magnetic field for supplying a voltage output dependent in magnitude upon the direction of said field relative thereto, an output coil, a frame, a pair of cores of magnetic material laterally spaced within said coil, each rotatably mounted on said frame, a continuous conductor having portions thereof wound in opposite directions on said cores to form oppositely acting exciting windings for producing flux flowing in opposite directions for instantaneous values thereof in said cores and having terminals thereof fixed respectively on said cores, a source of alternating current, and connecting means for supplying current to said conductor from said source, simultaneous rotation of said cores in opposite directions with the accompanying differential change in the number of turns in said windings providing an adjustment of the voltage induced in said output coil by current in said conductor whereby potentials of a frequency equal to that of said alternating current source will be substantially balanced out in said output coil while alternating voltages produced through interaction between said device and external field and of a frequency twice that of said alternating current source will be provided as a signal output by said output coil.

4. In a device sensitive to an external magnetic field for supplying a potential output dependent in magnitude upon the direction of said field relative thereto, an inductor comprising a pair of laterally spaced, elongated'core members of permeable magnetic material, an exciting coil on each core member, said exciting coils being so constructed and relatively arranged as to produce, when energizedirom a source of pulsating electrical energy, periodically varying flux flowing in instantaneously opposite directions in said core members, respectively, a pick-up winding comprising convolutions each encircling both of said core members, and means for differentially varying the components of voltage induced in said output coil by the currents in'said exciting coils whereby potentials of a frequency equal to the periodicity of said varying 'flux will be substantially balanced out in said pick-up winding while alternating'volt'ages produced through interaction between said device and an external field fleld for supplying a potential output dependent in magnitude upon the direction of said field relative thereto, an inductor comprising a pair of laterally spaced, elongated core members of permeable magnetic material, an exciting coil on each core member. said exciting coils being produce, when energized from a source of pulsating electrical energy, substantially equal periodically varying fluxes flowing in instantaneously opposite directions in said core members, respectively, a pick-up winding comprising convolutions each encircling both of said core members, and means for differentially varying the inductance between said exciting coils and said output coil whereby potentials of a frequency equal'to the periodicity of said varying flux will be substantially balanced out in said pick-up winding while alternating voltages produced through interaction between said device and an external field and of a frequency twice that of the periodicity of said flux will be provided as a signal output by said pick-up winding.

6. In a device sensitive to an external magnetic field for supplying a potential output dependent in magnitude upon the direction of said field relative thereto, an inductor comprising a pair of parallelly extending core members of permeable magnetic material, said members being of unequal length, means for producing a periodically varying flux flowing in relatively 3o opposite directions in said core members, respectively, for instantaneous values thereof, and a pick-up winding comprising convolutions each encircling both of said core members whereby potentials of a frequency equal to the periodicity of said varying flux will be substantially balanced out in said pick-up Winding while alternating voltages produced through interaction between said device and an external fleld and of a frequency twice that of the periodicity of said flux will be provided as a signal output by said pickup winding.-

'7. In a flux valve of the character described for supplying a potential output dependent in magnitude upon the direction of an external 5 magnetic field relative thereto, an inductor comprising a pair of laterally spaced, elongated core members of permeable magnetic material so relatively arranged that a first thereof extends axially beyond the second at an end thereof,

means for causing exciting fluxes to circulate through said inductor, and a pickup winding having convolutions extending about both core members.

8. Ina flux valve of the character described for supplying a potential output dependent in magnitude upon the direction of an external magnetic fleld relative thereto, a magnetic circuit in- 'cluding means for causing exciting fluxes to circulatethereabout and two core portions of permeable magnetic material arranged on opposite sides of said circuit so that respective exciting fluxes in said coreportions flow simultaneously in opposite directions, said circuit being so constructed and said core portions being so relatively arranged as to provide a leakage flux predominately of one of said directions of flow, and a pickup winding at least initially movable relative to at least one of said core, portions and having its convolutions extending about both thereof whereby the relative relation of said pickup winding to said leakage flux may be adjusted to reduce the voltage component of exciting frequency in the pickup winding.

9. A flux valve for use in a remote reading so constructed and relatively arranged as to" 1. larly disposedinductors each including a pair of laterally spaced, elongated core members of permeable magnetic material, means for producing a pulsating flux in the core members of each inductor, said flux flowing in the members of each inductor in respectively simultaneously opposite directions, and pick-up windings associated with each inductor and respectively comprising convolutions each encircling both core members of the inductors whereby potentials of a frequency equaito the periodicity of said varying flux will be substantially balanced out in said pick-up windings while alternating voltages produced through interaction between said inductors and an external field and of a frequency twice that of the periodicity of said fiux will be provided as a signal output by said pick-up windings, the pick-up windings of the inductors being connected together in polyphase fashion.

10. A fiux valvefor use in a remote reading compass system comprising three relatively angularly disposed inductors each including a pair of laterally spaced, elongated core members of permeable magnetic material, a coil on each core member adapted when energized from a source of periodically varying electrical energy to produce periodically varying flux in said core members, said flux flowing in said members in respectively, simultaneously opposite directions, and pick-up windings associated with each inductor and respectively comprising convolutions each encircling both core members of the inductors whereby potentials of a frequency equal to the periodicity of said'varying flux will be substantially balanced out in said pick-up windings while alternating voltages produced through interaction between said inductors and an external field and of a frequency twice that of the periodicity of said fiux will be provided as a signal output by said pick-up windings, the pick-up'windings of the three inductors being Y connected together across a three terminal output.

11. A fiux valve of the character recited in claim 9 in which the pick-up windings are Y connected together across a three terminal output.

12. An electrical inductive device for producing through interaction with a unidirectional magnetic field a three-circuit, variable alternating potential output and in which the alternating E. M. F. in each circuit varies with the orientation of the device in the magnetic field, said device comprising an inductor having three core legs of permeable magnetic material equi-angularly disposed with respect to one another in triangular fashion, coil means associated with said inductor and adapted to be connected with a source of single phase alternating current for producing periodically varying fluxes in said cores, and a pick-up coil associated with each core leg for generating varying potentials under the influence of said external field upon said core legs, said pick-up coils being Y connected in a three-circuit alternating output similar to that of a Selsyn of the device in the magnetic field, said device comprising an inductor having three substantially coplanar core legs of permeable magnetic material equi-angularly disposed with respect to one another in triangular fashion, coil means associated with said core legs and adapted to be connected with a source of single phase alternating current for producing periodically varying fluxes in said core legs, and a pick-up coil associated with each core leg for generating varying potentials under the influence of said external field upon said inductor, said pick-up coils being Y connected in a three-circuit alternating output similar to that of a Selsyntransmitter in which the generated potentials are of double the frequency of said source, whereby the output of said coils may be used to reproduce the position of said inductor in said magnetic field by connecting said output to an induction device of the Selsyn type supplied with double the frequency of said source.

LENNOX F. BEACH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re.18,'855 Flehr June 6, 1933 1,004,102 Storer Sept. 26, 1911 1,635,060 Thompson July 5, 1927 1,813,409 Kouyoumjian July 7, 1931 1,828,900 Kouyoumjian Oct. 27, 1931 1,998,209 Sundhausen Apr. 16, 1935 2,032,455 Williams Mar. 3, 1936 2,047,609 Antranikian July 14, 1936 2,158,500 Guerra May 16, 1939 2,241,499 Barth May 13, 1941 2,360,851 Curry Oct. 24, 1944 2,374,166 Beach et a1. Apr. 24, 1945 2,383,459 Beach Aug. 28, 1945 FOREIGN PATENTS Number Country Date 142,164 Great Britain May 6, 1920 451,850 Great Britain Aug. 10, 1936 OTHER REFERENCES 47, June 1936, Heft 6. 

